Glycidyl (epoxy) compounds are used in numerous applications in such fields as coating material, civil engineering and electrical material due to their superior electrical characteristics, adhesiveness and heat resistance. In particular, aromatic glycidyl (epoxy) compounds such as bisphenol A diglycidyl ethers, bisphenol F diglycidyl ethers, phenol novolak epoxy resins or cresol novolak epoxy resins are widely used in combination with various curing agents due to their superior water resistance, adhesiveness, mechanical properties, heat resistance, electrical insulating properties and economic feasibility.
Glycidyl compounds are molecularly designed so as to coincide with target properties in order to improve the physical properties of resins containing the glycidyl compounds and curing agents. In the case of bisphenol A diglycidyl ethers, for example, the optical characteristics (transparency) of cured products and fluidity during curing is known to improve as a result of hydrogenating aromatic rings at phenol moieties of the basic skeleton to derive an aliphatic cyclohexane skeleton. In the case of phenol novolak epoxy resins, fluidity during curing can be changed or heat resistance or adhesiveness and the like of cured products can be controlled by adjusting the degree of polymerization or molecular weight distribution of the glycidyl compound.
The introduction of multiple functional groups into glycidyl compounds is known as a technique for improving characteristics, such as the heat resistance or adhesiveness of cured resins containing a glycidyl compound and curing agent. The number of crosslinking reaction sites between a glycidyl compound and curing agent can be increased by increasing the density of reactive functional groups in the resin (amount of functional group contained per molecule). Since the crosslink density per unit volume of the cured product increases, molecular micro-motion is controlled and resistance of the cured product to external effects is enhanced. As a result, heat resistance of the cured product is improved and properties, such as rigidity or adhesiveness can be imparted to the cured product.
A known technique for introducing multiple functional groups into a glycidyl compound comprises introducing two or more glycidyl groups into an aromatic ring skeleton of a glycidyl compound having an aromatic ring skeleton to increase crosslink density. For example, Patent Document 1 (Japanese Unexamined Patent Publication No. S63-142019) discloses that polyvalent glycidyl compounds, having a glycidyl group at the ortho position or para position relative to a glycidyl ether group bonded to a phenol site of a compound having bisphenol for the basic skeleton thereof, have superior adhesiveness to metal, low hygroscopicity and favorable mechanical characteristics. These compounds are synthesized by using a phenol, such as bisphenol F, for the starting raw material, subjecting the phenolic hydroxyl group to 2-alkenylation, and subjecting the ortho position or para position to 2-alkenylation by Claisen rearrangement of the resulting 2-alkenyl ether group, followed by glycidyl etherification using epichlorohydrin and oxidation (glycidylation) of the side chain 2-alkenyl group.
However, in the oxidation (glycidylation) reaction during the final stage of the process, since an amount of an organic peroxide, such as peracetic acid, performic acid, m-chloroperbenzoic acid or peroxyphthalic acid, or an inorganic peroxide, such as permolybdic acid, pervanadic acid or pertungstic acid, is required that is equal to or greater than the chemical equivalent with respect to the reactive site in the form of a 2-alkenyl group, there were cases in which it was difficult to remove residues of these oxidizing agents from the target product, or the oxidizing agents were expensive and the process thus lacked industrial applicability. In addition, since epichlorohydrin is used in the synthesis process, in the case of producing compounds having a large number of functional groups, the content of organic chlorine compounds in the product increases as the amount of used epichlorohydrin increases.
In order to avoid contamination by organic chlorine compounds, it is effective to use a method that does not use epichlorohydrin when synthesizing glycidyl (epoxy) compounds. For example, one possible method for synthesizing polyvalent diglycidyl compounds having an aromatic ring skeleton comprises 2-alkenylation of the ortho position or para position by Claisen rearrangement of a 2-alkenyl phenyl ether, 2-alkenyl etherification of the resulting phenolic hydroxyl group, and simultaneous oxidation (glycidylation) of 2-alkenyl ether groups and 2-alkenyl groups at the ortho position or para position thereof. According to this method, the amount of chlorine in a glycidyl compound can be significantly reduced in principle since epichlorohydrin is not used. However, simultaneous oxidation of 2-alkenyl ether groups and 2-alkenyl groups at the ortho position or para position thereof has heretofore been unknown since it is typically difficult to control the reaction due to differences in reactivity between these groups.